This revised K01 career development application is designed to prepare Jennifer I. Manuel, Ph.D., for a productive career as an independent investigator who conducts research and advances knowledge in the development/adaptation and implementation of interventions that improve the lives of individuals with co- occurring substance use and mental health disorders. Under the primary mentorship of Dr. Dace Svikis, Dr. Manuel will receive formal mentoring and direct supervision, and complete formal (i.e., coursework) and informal (e.g., seminars, trainings, conferences) didactic training to increase her knowledge and skills in the following areas: (1) adaptation and implementation of evidence-based interventions; (2) participatory planning methods; (3) quantitative and qualitative methods and analyses; (4) grant writing and management; and (5) responsible conduct of research. The proposed research uses a multi-phase approach that strategically dovetails the applicant's training plan. Specifically, the applicant uses participatory planning methods to adapt and implement an established, nationally-recognized intervention, Critical Time Intervention, for a new population and setting among individuals with co-occurring substance use and mental health disorders who are vulnerable to relapse following residential substance abuse treatment. The specific aims are to: (1) identify challenges and strategies of community reentry among individuals with co-occurring disorders in residential substance abuse treatment and their professional (e.g., providers) and nonprofessional (e.g., family, friends, community members) supports; (2) adapt and translate CTI for individuals with co-occurring disorders during the transition from residential substance abuse treatment into the community, utilizing participatory planning methods; and (3) conduct a pilot study to examine the feasibility, acceptability, and preliminary outcomes of the adapted CTI compared to usual discharge planning services. The proposed research contributes to the candidate's career development, as it augments her existing experience in research coordination and secondary analysis through leading a study from the ground up and conducting primary data analysis, and yields pilot data for a subsequent R01 to test the effectiveness of the adapted CTI intervention on a larger scale. The participatory planning framework that guides this application, if successful, could be used to prepare interventions for other vulnerable populations and advance implementation science by developing a systematic approach for helping to close the gap between research and practice.